Intrinsic Fluorescence Decay Mechanisms of Proteins is a multi- investigator, multidisciplinary project combining time-resolved fluorescence with NMR and molecular modeling. Our objective is to determine how time-resolved fluorescence of the three aromatic amino acids tryptophan, tyrosine, and phenylalanine can be used to obtain information about structure and conformational dynamics of proteins. This requires understanding how and to what extent ground-state and excited-state processes affect the fluorescence intensity decay kinetics. NMR is being used to help define important ground-state processes. Molecular modeling, based on X- ray crystal structures, is being used to compute properties of an aromatic amino acid's local environment for comparison with the conclusions obtained from fluorescence and NMR. In this initial grant period we are investigating well-defined, simple peptide and polypeptide analogues having a single aromatic amino acid by systematically substituting in each aromatic amino acid at the same position in the peptide chain. These studies on peptides and polypeptides are the basis for extending the investigation into several structurally related single-tyrosine proteins. The results of this interdisciplinary approach, emphasizing tyrosine fluorescence, will be used, through a continuation application, to extend this investigation to tryptophan fluorescence of proteins. This work will further our understanding of the time-resolved fluorescence of the aromatic residues, add significantly to our knowledge of the solution structure and conformational dynamics of proteins, and make time-resolved fluorescence techniques a more powerful tool for analyzing protein structure.